Motor fuel



United States "atent 1 3,037,492 MOTOR FUEL Martin Hamel, Chicago, and Fred K. Kawahara, Park Forest, 111., and Russell H. Brown, Munster, Ind., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana N Drawing. Filed Feb. 27, 1959, Ser. No. 795,894 8 Claims. (Cl. 123-1) This invention relates to motor fuels characterized by their ability to suppress surface ignition in the operation of internal combustion engines. More particularly, the invention provides an improved motor fuel which is effective in suppressing surface ignition or preignition.

Current emphasis on high compression ratios and other high performance design features in gasoline engines of the internal combustion type has created a situation where random knock from surface ignition, often referred to as surface ignition or preignition, has become a limiting factor in engine design and operation. Knock induced by surface ignition appears to be a result of the use of organo-lead compounds, particularly tetraethyl lead, as the anti-knock agent in high octane number fuels. When these leaded motor fuels are burned in internal combustion engines, deposits of carbonaceous material and lead salts are continuously formed on the combustion chamber walls. Apparently surface ignition, that is, the ignition of the fuel-air mixture either before or after passage of the spark, is caused by glowing of the carbon in the deposits. It is generally believed that the presence of lead compounds in the deposits causes the carbon to glow at a significantly lower temperature than the glow point of carbon alone. i

It is well known that the addition of certain organic compounds of phosphorus, such as tricresylphosphate, to leaded fuels reduces surface ignition. Unfortunately, phosphorus compounds vary widely in effectiveness, and those that are most effective often have the undesirable property of lowering the octane number of the fuel. With petroleum refiners spending millions of dollars annually to improve the octane numbers of premium motor fuels, any substantial decrease in octane number is of course intolerable.

In accordance with the invention, an additive for use with leaded motor fuels has now been discovered which not only is outstandingly effective in reducing surface ignition or preignition, but, when employed in proper quantities, does not reduce the octane number of the fuel. Specifically, it has now been discovered that a hydroxyalkyl derivative of a cyclic dithiophosphoric acid, having the formula wherein the Y groups are each hydrogen atoms or alkyl radicals of 1-4 carbon atoms each, and Z is a hydrogen atom or an alkyl radical of 1-4 carbon atoms, is an outstanding preignition suppressant additive. This additive is incorporated into leaded hydrocarbon motor fuels of the gasoline boiling range in an amount sufiicient to provide a mol ratio of phosphorus to lead (MR P/Pb) of from about 0.01 to about 1.0, preferably about 0.020.20.

It has further been discovered, contrary to experience with many other organic compounds of phosphorus, that the inventive additives have no deleterious effect on the ability of motor fuels to resist the formation of oxidative gums on storage. In addition, the additives do not form troublesome deposits in the air-fuel induction system.

The motor fuel of the invention may contain tetraethyl lead (TEL) equivalent to a concentration of from about 0.5 ml. to about 5 ml. or more per gallon of the hydrocarbon motor fuel; the concentration of tetraethyl lead may be varied as is usual with the requirement of the engine.

The hydrocarbon component which constitutes the base of the fuel will preferably 'be gasoline but may be any other combustible liquid of suitable volatility commonly employed as fuel for internal-combustion spark ignition engines. Such liquids include paraflinic, naphthenic and aromatic hydrocarbons, pure hydrocarbons such as isooctane, and mixtures of isooctane with other suitable liquid hydrocarbons. whole or in part, from distillation of crude oil, catalytic or thermal cracking of gas oils, alkylation of isoparafiins with olefins, polymerization of olefins, etc. The boiling point of such fuels should be in the range of from about F. to about 500 F. and preferably in the range of from about F. to about 400 F. Motor fuels may also contain anti-oxidants, stabilizers, dyes, anti-icing agents, halogen-type lead scavenging agents and/or other compounds which are commonly employed in leaded motor fuels.

There can also be provided, in accordance with the invention, an additive suitable for incorporation into leaded motor fuels which comprises essentially the above described hydroxyalkyl derivative of a disubstituted thiophosphoric acid, either alone or with sufficient TEL to afford the proper MR P/ Pb. The additive may also contain an inert solvent, such as a refined hydrocarbon oil, and also desirable amounts of halo-hydrocarbon lead scavenging agents, dyes, and the like.

The defined additives, which are S-hydroxyalkyl derivatives of cyclic disubstituted dithiophosphoric acid, may be prepared by any of the conventional means known for preparing analogous compounds. Thus, appropriate diols, having two carbinol groups separated by a single carbon atom, may be reacted with phosphorus pentasulfide (P 5 to form a cyclic dithiophosphoiic acid, and then reacted with an a/S' epoxide. Typical examples of ap propriate diols include 2-methylpentanediol-2,4 (Y Y Y are methyl radicals), propanediol-l,3 (all Ys are hydrogen), 2-ethylhexanediol-l,3 (Y is propyl, Y is ethyl), pentanediol-2,4 (Y and Y are methyl), etc. Although the Y groups on the previously-defined structural formula may be hydrogen atoms or alkyl radicals of l-4 carbon atoms, it is preferred that there be at least one alkyl radical of 1-3 carbon atoms on at least two of the carbon atoms which ultimately form the cyclic structure. For instance, 2-methylpentanediol-2,4 reacts with P 8 to form 1,1,3-trimethyl cyclo trimethylene dithiophosphoric acid, which as a salt, can then be reacted with, say, 2-chloropropanol-l to form a compound of the invention where Y Y and Y are methyl groups and Y Y and Y and X are hydrogen atoms.

It is preferred, for reasons of convenience and economy, to react the cyclic dithiophosphoric acid with a 1,2-(or we) epoxy compound to form the inventive additive. Among the suitable epoxy compounds which can be used are ethylene oxide, propylene oxide, n-butylene oxide, etc.

As specific embodiments of the invention, the following examples are given. It is to be understood that these are These fuels may be derived, in

by way of illustration only and are not intended as a limitation of the invention:

EXAMPLE I EXAMPLE H The 1,1,3-trimethyl cyclo trimethylene hydroxyethyl dithiophosphate was tested, together with similar phosphorus additives, in an engine operated to determine surface ignition suppression effectiveness. This engine is a single cylinder, CFRL head engine, having a 7 to 1 compression ratio. Typical operating conditions for surface ignition or preignition studies are as follows:

Test duration 50 hours. Coolant temperature 148 F. Oil temperature 160 F. Air to fuel ratio 13/1.

For this test the engine is cycled as follows:

CYCLE CONDITIONS Time, Seconds 45 135 Rpm 600 900 Load None Full Surface ignition prevention effectiveness was determined using a premium fuel having 3 cc. of TEL per gallon and incorporated therewith the additive undergoing test.

The test data in the above table demonstrate the superiority of the present additive over similar phosphorus compounds with respect to surface ignition control. It will be noted that the additive may be employed at one-fourth to one-half the concentration of hitherto known preignition suppressants.

EXAMPLE III It was previously indicated that a major advantage of the inventive additive is its ability to substantially maintain the octane number of leaded gasolines. This is in marked contrast to other known phosphorusand sulfurcontaining additives, which decrease the octane number of gasolines. To demonstate this, tests were made in a CPR-L engine at various concentrations of several additives in a 94-96 octane number motor fuel, containing 3.0 cc. TEL per gallon. The following results were observed.

4 Table II OCTANE NUMBER CHANGE Concentration, MR P/Pb Test Additive 1 1,1,3 trimethylcyelotrimeth- +0.04 O N 0.12 O.N.

ylcne S-hydroxypropyl d1- thiophosphate. 2 0,0di-i-propy1-S-beta hy- 0.30 -0.50

droxethyl dithiophosphate. 3 1,1,3 trimethyleyclotrimetn -0.01 0.28

ylene S'alpha. phenylethyl dithiophosphate. 4. 'lricresyl phosphate 5 Dimethyl xylyl phosphate.

EXAMPLE IV A surprising benefit attendant with the present additives is their property of not accelerating oxidative gum formation on long term storage. This was demonstrated by testing motor fuels at accelerated oxidizing conditions of 212 F. and p.s.i.g. oxygen pressure, and noting the time (induction period) before rapid oxygen consumption occurred. The following results were observed with the additive of Example I.

Table III Induction Additive Concentration Period,

minutes Nil 425 0.13 MR P/Pb 425 EXAMPLE V The additive of Example 1 was also tested to determine any tendency to form deposits in the fuel induction system of an engine. This test involves running an aircooled Lauson single-cylinder engine on 6 gallons of gasoline containing 3.0 cc. TEL/gallon and 0.33 MR P/Pb. When the fuel is exhausted, the engine is dismantled and the intake manifold and valves are inspected. This fuel rated pass.

The percentages given herein and in the appended claims are weight percentages unless otherwise noted.

While the invention has been described by reference to specific embodiments thereof, the same are given by way of illustration. Modifications and variations will be apparent to those skilled in the art.

We claim:

1. A hydrocarbon motor fuel of the gasoline boiling range adapted for spark-ignition internal-combustion engines containing a minor amount of tetraethyl lead and, in combination therewith, in an amount sufficient to provide a mol ratio of phosphorus to lead of from about 0.01

to about 1.0, a hydroxyalkyl derivative of a cyclic dithiophosphoric acid, having the formula wherein the Y and Z groups are each selected from the group consisting of hydrogen atoms and alkyl groups of 1-4 carbon atoms each.

2. The fuel of claim 1 wherein the minor amount of tetraethyl lead is in the range of about 0.5 to about 5.0 cc. per gallon of fuel.

3. The fuel of claim 1 wherein Y Y and Y are methyl radicals and Y Y and Y are hydrogen atoms.

4. The fuel of claim 1 wherein Z is a methyl radical.

5. A hydrocarbon motor fuel of the gasoline boiling range adapted for spark-ignition internal-combustion engines Containing from 0.5 to 5.0 cc. tetraethyl lead per gallon of fuel and, in an amount sufiicient to provide a mol ratio of phosphorus to lead of from about 0.01 to about 1.0, 1,1,3-trimethyl cyclo trimethylene hydroxypropyl dithiophosphate.

6. An additive concentrate suitable for incorporation in leaded hydrocarbon motor fuels of the gasoline boiling range for spark-ignition internal-combustion engines, said additive concentrate consisting essentially of tetraethyl lead, and a hydroxyalkyl derivative of a cyclic dithiophosphoric acid, having the formula wherein the Y and Z groups are each selected from the group consisting of hydrogen atoms and alkyl groups of l4 carbon atoms each, said phosphorus compound be ing present to give a mol ratio of phosphorus to lead in the range of from about 0.01 to about 1.0.

7. The composition of claim 6 wherein said derivative is 1,1,3 trimethyl cyclo trimethylene hydroxypropyl dithiophosphate.

8. In the method of operating spark-ignition internal combustion engines, the improvement which comprises supplying to said engines a hydrocarbon motor fuel of the gasoline boiling range containing a minor amount of tetraethyl lead and, in combination therewith, in an amount sufficient to provide a mol ratio of phosphorus to lead of from about 0.01 to about 1.0, a hydroXyalkyl derivative of a cyclic dithiophosphoric acid, having the formula wherein the Y and Z groups are each selected from the group consisting of hydrogen atoms and alkyl groups of l-4 carbon atoms each.

References Cited in the file of this patent UNITED STATES PATENTS 2,783,204 McDermott Feb. 26, 1957 2,794,719 Bartleson June 4, 1957 2,794,720 Bartleson June 4, 1957 2,826,550 McDermott Mar. 11, 1958 

8. IN THE METHOD OF OPERATING SPARK-IGNITION INTERNAL COMBUSTION ENGINES, THE IMPROVEMENT WHICH COMPRISES SUPPLYING TO SAID ENGINES A HYDROCABON MOTOR FUEL OF THE GASOLINE BOILING RANGE CONTAINING A MINOR AMOUNT OF TETRAETHYL LEAD AND, IN COMBINATION THEREWITH, IN AN AMOUNT SUFFICIENT TO PROVIDE A MOL RATIO OF PHOSPHORUS TO LEAD OF FROM ABOUT 0.01 TO ABOUT 1.0, A HYDROXYALKYL DERIVATIVE OF A CYCLIC DITHIOPHOSPHORIC ACID, HAVING THE FORMULA 